This invention relates to a titanium-tungsten (titanium-tungsten) target material used to form a barrier metal layer or the like for use in semiconductor devices and to a method of manufacturing the titanium-tungsten target material.
With the increase in the degree of integration of large scale integrated circuits (LSIs), the need for a barrier metal layer as a means for avoiding aluminum wiring migration has arisen.
A titanium-tungsten thin film (typically composed of 10 wt % of titanium and the balance of tungsten) is often used as a barrier metal layer, and a method of sputtering a target is adopted to form such a titanium-tungsten thin film.
In general, a titanium-tungsten target material for the thin film is manufactured by blending a titanium powder and a tungsten powder and hot-pressing the blended powder.
However, no titanium-tungsten target having a suitably low oxygen content has been provided because a titanium powder used as a raw material for the conventional titanium-tungsten targets essentially have a large oxygen content, and also because the titanium powder is contaminated by oxygen when the titanium powder is milled more finely.
High-oxygen-content targets are disadvantageous because oxygen is liberated during sputtering to cause cracks in the target, oxidation of formed films, and variations in film quality.
Methods for reducing the oxygen content of a titanium-tungsten target are disclosed in U.S. Pat. No. 4,838,935 and JP-A-63-303017. In these methods, a hydrogenated titanium powder is used instead of the ordinary titanium powder.
The use itself of the hydrogenated titanium powder is effective in preventing oxidation and is also capable of limiting the amount of oxygen picked up during milling because the hydrogenated titanium powder may be more suitably milled with less contamination by oxygen as compared with the ordinary titanium powder.
It has thus become possible to obtain titanium-tungsten targets having an oxygen concentration as low as 900 pm or less.
Recently, with the development of semiconductor products having thinner conductors formed at a higher density, a new problem has arisen with respect to a sputtering process using the above-mentioned low-oxygen-concentration titanium-tungsten target in that large particles attach to a thin film formed by sputtering to cause disconnection of electrode wiring conductors.
The generation of such particles cannot be prevented as long as only the method for reducing the titanium-tungsten target oxygen content is used. It is supposed that the generation of such particles relates to coarse titanium grains existing in the titanium-tungsten target structure and segregation of titanium therein.
The inventor of the present invention has examined in detail the relationship between the target structure and the generation of particles, and has found that coarse titanium grains relate particularly to the generation of the particles. That is, titanium having an atomic weight lighter than that of tungsten is selectively sputtered faster so that cavities are formed in places where titanium has existed. Tungsten grains which have been surrounded by coarse titanium grains or groups of coarse titanium grains or located in the vicinity of coarse titanium particles are therefore scattered as large particles from the target material. The inventor has found this phenomenon as a cause of the generation of particles.